"Our trained officers have examined a huge amount of pictures and video footage sent in by festival goers and have determined that this woman may well be of assistance to our investigation.

"The time at which she was photographed, the area she was stood, the direction she was facing and the fact she seems to taking a video or pictures of the area where Robert was standing all suggest that she may well have captured a picture of the man responsible or the people he was with.

"Obviously, obtaining evidence such as that would represent a big step forward in this investigation and take us closer to catching the man responsible for this attack.

"I would urge her, or indeed any of the other three people pictured, to come forward and speak to us as soon as possible.

"One thing we have learned from speaking to the other eight witnesses is that any small piece of information could potentially prove useful to Police.

"One of those witnesses did not come forward initially as they believed that they would not be able to provide anything new to the investigation, which was simply not the case.

"Their witness statements provided new details that were previously unknown to officers, which proves that no piece of information is too small and that it is vital for witnesses to come forward should they think they know anything at all about the attack."

Appeal for this witness to come forward after Parklife death Credit: Greater Manchester Police

Credit: Greater Manchester Police

Robert Hart was assaulted at the music festival in Heaton Park in June he died five days later in hospital. He had been at the Parklife festival with his girlfriend Gemma Parry, after Gemma is now urging witnesses identified by police to come forward urgently.

"Despite the best efforts of GMP officers, Rob's family and myself to persuade him to do so, it is becoming less and less likely that the man responsible for his death is going to come forward of his own accord.

That makes these potential witnesses all the more important, as they may well hold the key for Police to track down the man who took Rob away from me, from his mother, brother, sisters, nieces and nephews.

I am now speaking to the woman pictured in the flat cap, or any of the other witnesses officers want to speak to, please contact Police.

Imagine if it was your husband, your boyfriend, your brother or son, try to imagine our suffering, knowing that the man that stole our beautiful Rob away from us may never be brought to justice.

You can make a difference.

"You might be able to help provide us with the closure we so desperately need, that Rob so desperately deserves. Please."

– Gemma Parry, Robert Hart's girlfriend

Robert Hart and Gemma Parry at the Parklife Festival in June Credit: Greater Manchester Police